A wide variety of wireless communication techniques have been developed to facilitate wireless telecommunication. In this disclosure, a wireless communication device (WCD) refers to any device that can modulate wireless signals as described in greater detail below. Some example WCDs include cellular or satellite radiotelephones, radiotelephone base stations, computers that support one or more wireless networking standards, wireless access points for wireless networking, PCMCIA cards incorporated within portable computers, direct two-way communication devices, personal digital assistants (PDAs) equipped with wireless communication capabilities, and the like.
In wireless telecommunication, information is modulated to create one or more baseband waveforms (also referred to as baseband signals). The baseband waveforms may then be mixed with an electromagnetic carrier wave (sometime referred to as an up-conversion process), and the carrier wave mixed with the modulated baseband waveform can be wirelessly transmitted to a receiving device. The receiving device mixes the baseband waveform from the received carrier wave (sometimes referred to as a down-conversion process). Demodulation of the baseband waveform can then be performed by the receiving device to obtain the modulated information.
A number of different modulation techniques have been developed for modulating information in order to facilitate wireless communication. One modulation technique commonly used in telecommunication systems is referred to as Gaussian minimum shift keying (GMSK) modulation. GMSK modulation is a binary modulation scheme that can be viewed as a derivative of minimum shift keying (MSK) modulation. MSK modulation is a type of continuous phase frequency shift keying (CPFSK) with a modulation index corresponding to the minimum frequency spacing that allows two FSK signals to be coherently orthogonal.
In GMSK, the sidelobe levels of the MSK modulated waveform are further reduced, e.g., by passing the waveform through a Gaussian filter. Gaussian filtering can smooth the phase trajectory of the MSK modulated signal and stabilize instantaneous frequency variations over time. In addition, the Gaussian filtering typically causes intersymbol interdependence in the waveform, e.g., making the value of one symbol dependent on the values of other symbols. GMSK modulation is an attractive candidate for wireless telecommunication because it generally exhibits excellent power efficiency and excellent spectral efficiency.
For example, GMSK modulation has been used in digital cellular communication standards including the global system for mobile communications (GSM) standardized by the European Telecommunication Standards Institute (ETSI). In addition, GMSK modulation has been used in various wireless networking systems, as well as other telecommunication systems.